Physiology-Based Electrocardiographic Criteria for Left Bundle Branch Capture

Abstract Background During left bundle branch (LBB) area pacing, it is important to confirm that the capture of the LBB is achieved, not just the capture of only the adjacent left ventricular myocardium (LV septal capture). Our aim was to establish ECG criteria for LBB capture by analyzing ECGs with confirmed LBB capture and non-capture. We hypothesized that since LBB pacing results in physiologic depolarization of the left ventricle then the native QRS can serve as a reference for the diagnosis of LBB capture in the same patient. Methods Only patients with direct evidence of LBB capture (output-dependent or refractoriness-dependent QRS morphology transition) were included. Several QRS characteristics were compared between the native rhythm and different types of LBB area capture. Receiver-operator characteristics analysis was performed to determine the optimal V6 R-wave peak time (RWPT) cut-off for LBB diagnosis. Results A total of 357 ECG tracing (124 patients) were analyzed: 118 with native rhythm, 124 with non-selective LBB capture, 69 with selective LBB capture and 46 with LV septal capture. Our hypotheses that during LBB capture the paced V6 RWPT (measured from QRS onset) equals the native V6 RWPT and that the paced V6 RWPT (measured from the stimulus) equals the LBB potential to V6 R-wave peak interval were positively validated. Criteria based on these rules had sensitivity and specificity of 98.0–88.2% and 85.7–95.4%, respectively. The optimal and 100% specific V6 RWPT values for differentiation between LBB capture and LV septal capture in patients with narrow QRS / right bundle branch block were 83 ms and 74 ms, respectively; while in patients with left bundle branch block/asystole/ventricular escape the optimal and 100% specific V6 RWPT values were 101 ms and 80 ms, respectively. Conclusions Novel criteria for LBB capture were developed and optimal V6 RWPT cut-offs were determined. What this study adds We showed that LBB pacing truly reproduce the physiological depolarization of the left ventricle since the paced V6 RWPT equals the native conduction V6 RWPT. Individualized LBB capture criteria, that use the native QRS as a reference, were developed. The optimal V6 RWPT values for differentiation between LBB capture and LV septal capture were determined, separately for patients with healthy and diseased LBB.